@silverwizard
Great idea! And you are not alone.
It is being done. No need to think about it so much, just do it.
There might already be a network in your area, all you need to participate might be a (reasonably) affordable LoRa radio. Take a look at #reticulum.
Apart from reticulum as a complete departure from traditional internet, all the #fediverse tech will "work" in isolation, there is no need for "internet".
humble advice:
Possible stumbling point in my experience is thinking in terms of "Internet". Don't compare or try to replicate.
Size does not matter. >1 is a "network". so it does not need to scale, but it does need a purpose. It might be good to pre define WHAT it is and WHY it exists, then you can hopefully attract like minded participants and avoid those who may damage the project.
Beyond initial outlay, fibre rollout is maybe not as costly as might be imagined. Running the fibre optic cable might be an issue in your locality however, but maybe worth looking into.
@silverwizard
People on the thread might get something from this talk: